An existing audio interface generally includes an audio output pin AUDIO, a ground pin GND and a microphone pin MIC. The audio output pin AUDIO generally includes a left-channel pin and/or a right-channel pin which normally are a third pin and a fourth pin of a four-section audio interface. There are two types of line sequences between a first pin and a second pin of the audio interface. As one type, the first pin is the microphone pin MIC, and the second pin is the ground pin GND. As the other type, the first pin is the ground pin GND, and the second pin is the microphone pin MIC.
When the audio interface is transmitting data, downlink audio signals are transmitted by an audio output pin AUDIO which may be one or both of the left-channel pin and the right-channel pin, while uplink audio signals are transmitted by the microphone pin MIC.
If not measured, a line sequence of the first pin and the second pin of an existing audio interface is unknown. Therefore, when transmitting an uplink audio signal, the line sequence of the first pin and the second pin of the audio interface needs to be measured so as to obtain the microphone pin MIC for transmitting the uplink audio signal. Measuring the line sequence of the first pin and the second pin of the audio interface requires extra works and is not convenient.
Thus, a device that ensures transmission of an uplink audio signal in case the line sequence of the audio interface is unknown is required.